JP2012079813A - Manufacturing method of electric storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an electric storage device capable of sufficiently impregnating an ionic liquid into the inside of a pore of an active material layer.SOLUTION: A manufacturing method of an electric storage device includes an impregnation step of impregnating an electrolytic solution into an opposed active material layer via a separator. The impregnation step comprises: a mixed electrolytic solution impregnation step of impregnating a mixed electrolytic solution of an ionic liquid and a high vapor pressure organic solvent having compatibility with the ionic liquid, a surface tension lower than the ionic liquid and a vapor pressure higher than the ionic liquid into the active material layer; and a removal step of removing a part or the whole of the high vapor pressure organic solvent from the impregnated mixed electrolytic solution.

Description

  The present invention relates to a method for manufacturing an electricity storage device.

Conventionally, as an electrolyte salt of an electric double layer capacitor, tetraethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₄ NBF ₄ ), triethylmethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₃ CH ₃ NBF ₄ ) Etc. are used. Moreover, as electrolyte salt of a nonaqueous electrolyte secondary battery, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), bis (trifluoromethanesulfonyl) imide lithium (LiN (CF ₃₎ SO ₂ ) ₂ ) and the like are used. On the other hand, carbonates such as propylene carbonate and diethyl carbonate, acetonitrile, and the like are known as solvents for non-aqueous electrolyte secondary batteries and electric double layer capacitors. Furthermore, in recent years, ionic liquids such as 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-ethyl-3methylimidazolium bis (trifluoromethanesulfonyl) imide, which are electrolyte salts but behave like liquids. However, for an electricity storage device such as an electric double layer capacitor, and for a non-aqueous electrolyte secondary battery, ionic liquid includes lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), bis It has been proposed to add (trifluoromethanesulfonyl) imidolithium (LiN (CF ₃ SO ₂ ) ₂ ) or the like.

  Electric storage devices such as electric double layer capacitors are required to be reliable at high temperatures so that they do not swell when used in high-temperature environments. Use low vapor pressure electrolytes. Is effective. As such a low vapor pressure electrolytic solution, for example, an ionic liquid as disclosed in Patent Document 1 is used. Since the ionic liquid is composed only of cations and anions, the boiling point is high and the temperature range in which the liquid state can be maintained is very wide. Furthermore, since the ionic liquid has almost no vapor pressure, the flammability is low and the thermal stability is very excellent.

JP 2007-227940 A

  However, when a low vapor pressure electrolyte such as an ionic liquid is used, because it has poor wettability with the active material used for the electrode, it is difficult to sufficiently penetrate and contact the pores of the active material layer, There was a problem that the capacity was lowered.

  In view of the above, an object of the present invention is to provide a method for manufacturing an electricity storage device that can sufficiently penetrate an ionic liquid into the pores of an active material layer.

In order to achieve the above object, a method for producing an electricity storage device according to the present invention is a method for producing an electricity storage device including an impregnation step of impregnating an electrolyte into an active material layer,
The impregnation step comprises:
Mixing which infiltrates the active material layer with a mixed electrolyte of an ionic liquid and a high vapor pressure organic solvent that is compatible with the ionic liquid and has a lower surface tension than the ionic liquid and a higher vapor pressure than the ionic liquid An electrolytic solution impregnation step;
Removing a part or all of the high vapor pressure organic solvent from the permeated mixed electrolyte,
In the mixed electrolyte impregnation step, the content of the high vapor pressure organic solvent in the mixed electrolyte is adjusted to 5 vol% or more and 50 vol% or less,
The removal step is characterized in that the removal is performed so that the content of the high vapor pressure organic solvent in the mixed electrolyte is 1% by weight or less.
According to the method of manufacturing the electricity storage device according to the present invention configured as described above, the ionic liquid is sufficiently infiltrated into the pores of the active material layer and brought into contact with the ionic liquid. The high vapor pressure organic solvent can be partially or completely removed while maintaining the contact state.

Moreover, in the manufacturing method of the electrical storage device which concerns on this invention, content of the said high vapor pressure organic solvent in the said mixed electrolyte solution is adjusted to 5 volume% or more and 50 volume% or less.
Thus, the said mixed electrolyte and an active material layer can be made to contact effectively by making content of the said high vapor pressure organic solvent in the said mixed electrolyte into 5 volume% or more.
Further, by setting the content of the high vapor pressure organic solvent in the mixed electrolyte to 50% by volume or less, the ionic liquid in the mixed electrolyte can be easily permeated into the active material layer, and compared. The high vapor pressure organic solvent can be removed in a short time.

  Furthermore, in the method for manufacturing an electricity storage device according to the present invention, the removal step is performed such that the content of the high vapor pressure organic solvent in the mixed electrolytic solution is 1% by weight or less. Thereby, the swelling at high temperature in an electrical storage device can be suppressed effectively.

  In the method for manufacturing an electricity storage device according to the present invention, it is preferable to use a high vapor pressure organic solvent having a vapor pressure of 8.5 kPa or higher at 20 ° C., thereby making it possible to increase the vapor pressure difference from the ionic liquid. Therefore, it becomes easy to remove the high vapor pressure organic solvent preferentially, and the removal time can be shortened.

  In the method for producing an electricity storage device according to the present invention, it is preferable to use a high vapor pressure organic solvent having a boiling point of 80 ° C. or less, whereby the boiling point difference from the ionic liquid can be increased, and the high vapor pressure organic solvent is preferentially used. It becomes easy to remove, and the removal time can be shortened.

  In the method for producing an electricity storage device according to the present invention, it is preferable to use a high vapor pressure organic solvent having a molecular weight of 88.1 or less. This facilitates the preferential removal of the high vapor pressure organic solvent, and reduces the removal time. Can be shortened.

  In the method for producing an electricity storage device according to the present invention, it is preferable to use a high vapor pressure organic solvent having a surface tension at 25 ° C. of 24.4 mN / m or less, whereby the ionic liquid is activated together with the high vapor pressure organic solvent. It is possible to sufficiently penetrate the material layer.

  In the method for producing an electricity storage device according to the present invention, methyl propionate or acetone can be preferably used as the high vapor pressure organic solvent.

As described above, according to the method for manufacturing an electricity storage device according to the present invention, after the ionic liquid is sufficiently infiltrated into the pores of the active material layer, the ionic liquid is sufficiently in contact with the active material layer. The high vapor pressure organic solvent can be partially or completely removed while maintaining the above.
Therefore, the ionic liquid can be sufficiently permeated into the pores of the active material layer by the method for manufacturing the electricity storage device according to the present invention.

1 is a cross-sectional view schematically showing a state in which an electrolytic solution 2 is permeated into pores of an active material layer 1 through a manufacturing method according to an embodiment of the present invention. It is sectional drawing which shows typically the state which made the electrolyte solution 2 osmose | permeate the inside of the pore of the active material layer 1 through the conventional manufacturing method. In the manufacturing method of the Example which concerns on this invention, it is process drawing which produces a cell assembly. FIG. 4 is a process diagram for producing an electric double layer capacitor using the cell assembly of FIG.

Hereinafter, the manufacturing method of the electrical storage device of embodiment which concerns on this invention is demonstrated, referring drawings.
Note that in this specification, the power storage device includes a lithium ion secondary battery, a lithium ion capacitor, and the like in addition to the electric double layer capacitor described in the examples described later.
In general, a method for producing an electricity storage device includes injecting an electrolyte solution between a positive electrode and a negative electrode facing each other through a separator, and infiltrating the electrolyte solution into an active material layer of the separator, the positive electrode, and the negative electrode. In the method for manufacturing the electricity storage device of this embodiment,
(I) As an electrolytic solution, a mixed electrolytic solution of an ionic liquid and a high vapor pressure organic solvent having a higher vapor pressure than the ionic liquid is used.
(Ii) A mixed electrolytic solution of an ionic liquid and a high vapor pressure organic solvent is injected between the positive electrode and the negative electrode, and the electrolytic solution is infiltrated into the active material layer of the separator, the positive electrode, and the negative electrode. This is different from the conventional one in that part or all of the organic solvent is removed.

Here, in the present embodiment, the high vapor pressure organic solvent used together with the ionic liquid is compatible with the ionic liquid, has a lower surface tension at 25 ° C. than the ionic liquid, and a vapor pressure at 20 ° C. than the ionic liquid. Use high vapor pressure organic solvents.
Thus, the manufacturing method of this embodiment mixes an ionic liquid with a high vapor pressure organic solvent such as methylpropionate or acetone, and injects it into the active material layers and separators of the positive electrode and the negative electrode. After sufficiently infiltrating, an electricity storage device is manufactured through a step of removing only part or all of the high vapor pressure organic solvent.

In the present embodiment, by using a mixed electrolyte obtained by mixing an ionic liquid and a high vapor pressure organic solvent, the wettability of the mixed electrolyte with respect to the active material layer and the separator is improved, and the ions contained in the mixed electrolyte The liquid penetrates sufficiently into the pores of the active material layer.
That is, the ionic liquid has a large surface tension and a large molecular weight, so that the viscosity is high and the wettability with the active material is poor. The wettability is improved, and the ionic liquid contained in the mixed electrolyte can sufficiently penetrate into the pores of the active material layer.
As described above, after the ionic liquid has sufficiently penetrated into the pores of the active material layer, for example, when dried under reduced pressure, the high vapor pressure organic solvent remains with the ionic liquid remaining inside the pores of the active material layer. Selectively removed.

As described above, as shown in FIG. 1, the electrolyte solution 2 made of only the ionic liquid or having the ionic liquid as a main component sufficiently penetrates into the pores of the active material layer 1 and has a wider area. 1 can be achieved.
On the other hand, even if an attempt is made to penetrate the pores of the active material layer 1 with only the ionic liquid without mixing with the high vapor pressure organic solvent, as shown in FIG. It is difficult to sufficiently penetrate the pores, and it is difficult to ensure a sufficient contact area with the active material layer 1.

Hereinafter, the manufacturing method of this embodiment will be described in more detail.
In the present embodiment, the high vapor pressure organic solvent needs to have better wettability than the ionic liquid. In other words, the contact angle of the high vapor pressure organic solvent with respect to the active material is the active angle of the ionic liquid. It is required to be smaller than the contact angle to the substance.
Further, the molecular weight of the high vapor pressure organic solvent is preferably lower than the molecular weight of the ionic liquid. The lower the molecular weight, the easier it is to volatilize, and in the step of removing the high vapor pressure organic solvent, the polymer solvent can be easily selectively removed, and the production efficiency can be increased.
Furthermore, the decomposition voltage of the high vapor pressure organic solvent is preferably wider than the operating voltage range of the electricity storage device. This is because when the remaining high vapor pressure organic solvent is electrolyzed, gas is generated, leading to expansion of the electricity storage device. Specifically, it is preferably 5.2 V to −3.0 V with respect to the standard hydrogen electrode potential.

  Regarding the combination of the ionic liquid and the high vapor pressure organic solvent, the ionic liquid is not particularly limited. For example, 1-ethyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3methylimidazolium bis ( (Trifluoromethanesulfonyl) imide, or a mixed electrolytic solution thereof.

  Further, the high vapor pressure organic solvent is not particularly limited, and examples thereof include propylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, dimethoxymethane, 1,3-dimethoxymethane, tetrahydrofuran, 2- Methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, acetonitrile, 3-methyl sulfolane, N , N-dimethylformamide, acetone, or a mixed electrolytic solution thereof can be used.

  More preferably, 1-ethyl-3-methylimidazolium tetrafluoroborate is used as the ionic liquid. Since 1-ethyl-3-methylimidazolium tetrafluoroborate has a smaller ionic radius of tetrafluoroborate, which is an anion, compared to 1-ethyl-3methylimidazolium bis (trifluoromethanesulfonyl) imide, it conducts more ions. This is because an electric double layer capacitor having a high conductivity and a lower resistance can be supplied.

The high vapor pressure organic solvent is preferably propylene carbonate, γ-butyrolactone, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, acetonitrile, or acetone. More preferably, methyl acetate, methyl propionate or acetone such as CH ₃ —COO—R (—R: a substituent having 2 or less carbon atoms) is used. Methyl acetate, methyl propionate or acetone such as CH ₃ —COO—R (—R: a substituent having 2 or less carbon atoms) is compatible with the ionic liquid and has a low boiling point (methyl acetate ( In the step of removing boiling point 58 ° C., molecular weight 74.1), methyl propionate (boiling point 79.7 ° C., molecular weight 88.1), acetone (boiling point 57 ° C., molecular weight 58.1)), high vapor pressure organic solvent. This is because it can be removed more easily and the effects of the present invention can be further exhibited.

  In the mixed electrolyte containing the ionic liquid and the high vapor pressure organic solvent, the content of the high vapor pressure organic solvent after removing the high vapor pressure organic solvent is preferably 5% by weight or less, more preferably 1 Less than wt%. Thereby, the swelling at high temperature in an electrical storage device can be suppressed effectively.

In addition, examples of the method for volatilizing and removing the high vapor pressure organic solvent include a removal method by heating, decompression, or a combination thereof.
Moreover, it is preferable that the boiling point difference of the boiling point of an ionic liquid and the boiling point of a high vapor pressure organic solvent is 50 degreeC or more. When the difference in boiling points is 50 ° C. or more, the high vapor pressure organic solvent can be easily removed by volatilization.

According to the manufacturing method of the present embodiment described above, the ionic liquid sufficiently contacts the surface of the active material layer inside the pores of the active material layer, the capacity of the electric double layer capacitor increases, and the internal resistance decreases. Since the high vapor pressure organic solvent is partially removed, it is possible to provide a highly reliable electric double layer capacitor in which swelling at a high temperature is suppressed as compared with the case where this removal operation is not performed.
Therefore, according to the manufacturing method of this embodiment, it is possible to manufacture an electricity storage device having excellent electrochemical characteristics and high reliability.
In the above description of the embodiment, an example in which an electric double layer capacitor is produced by impregnating a separator with an ionic liquid has been described. However, the present invention is not limited to this, and an ion can be used without using a separator. The present invention can also be applied to a case where a gel impregnated with a liquid is used between electrodes.

The electric double layer capacitor cells of Examples 1 to 4 according to the present invention and the electric double layer capacitor cells of Comparative Examples 1 to 4 were produced and compared. The structures of the electric double layer capacitor cells of the example and the comparative example were the same, and the electrolytic solution and the manufacturing method were changed to be examples 1 to 4 and comparative examples 1 to 4, respectively.
And in the electric double layer capacitor | condenser of Examples 1-4 and Comparative Examples 1-4, the cell was produced as follows and the electrochemical measurement was performed.

<Production of electric double layer capacitor cell>
1. Preparation of electrodes
(I) 29.0 g of activated carbon (BET specific surface area 1668 m ² / g, average pore diameter 1.83 nm, average particle diameter D50 = 1.26 μm),
The BET specific surface area and average pore diameter were calculated by the BET method by N ₂ gas adsorption / desorption using “BELmax manufactured by Shimadzu Corporation”, and the average particle diameter was measured by a laser diffraction method. .
(Ii) 2.7 g of carbon black (Toka Black # 3855 manufactured by Tokai Carbon Co., Ltd., BET specific surface area 90 (m ^{2 /} g)),
(Iii) 3.0 g of carboxymethyl cellulose (CMC2260 manufactured by Daicel Chemical Industries, Ltd.)
(Iv) 2.0 g of a 38.8 wt% polyacrylate resin aqueous solution,
(V) 286 g of deionized water,
Were weighed, mixed under primary dispersion and secondary dispersion under the conditions shown in Table 1.
Then, it applied on aluminum foil (thickness 20 micrometers) by the doctor blade method on the conditions shown in Table 1, and produced the electrode sheet.

Table 1

The electrode sheet produced as described above was punched out to produce a positive electrode plate 10 shown in FIG. 3A and a negative electrode plate 20 shown in FIG. Each of the positive electrode plate 10 and the negative electrode plate 20 includes activated carbon coating portions 11 and 21 and lead portions 12 and 22.
Here, a Thomson blade [N4Z235-0010 made by Mitsuwa Frontech] is used for electrode punching, and the positive electrode plate 10 has an activated carbon coating portion 11 of 10 × 10 mm, and the negative electrode plate 20 has an activated carbon coating portion 21 of 12. Punched out to be × 12 mm.
The lead portion 12 of the positive electrode plate 10 and the lead portion 22 of the negative electrode plate 20 were 2 mm wide and 9 mm long, respectively.

2. Preparation of Separator An aramid separator 30 having a thickness of 23 μm shown in FIG.
The size of the aramid separator 30 was 15 mm × 15 mm.

3. Cell Assembly Assembly As shown in FIG. 3 (d), an aramid separator 30 is disposed between the positive electrode plate 10 and the negative electrode plate 20, and as shown in FIG. 3 (e), the Kapton tape 41 is used to connect the positive electrode plate 10 and the aramid. The laminated body 40 was produced by bonding the separators 30 and the anode plate 20 and the aramid separator 30 together.
As shown in FIG. 3 (e), a positive electrode aluminum tab 51 and a negative electrode aluminum tab 52 are attached to the lead portion 12 of the positive electrode plate 10 and the lead portion 22 of the negative electrode plate 20 of the laminate 40 with a Kapton tape 42, respectively. The cell assembly 50 was manufactured by conducting conduction by ultrasonic welding in the conduction part 55 at the location. In FIG. 3 (e), the sealant 53 is made of, for example, polypropylene, and is provided to ensure airtightness between the positive electrode aluminum tab 51 and the negative electrode aluminum tab 52 and an aluminum laminate film 60 described later.

4). Lamination / Liquid Injection As shown in FIG. 4 (a), the cell assembly 50 is wrapped from both sides with an aluminum laminate film 60 having an aluminum foil as a core material and a resin layer on both sides, and a seal portion S1, a seal portion S2, and a seal portion S3. Was temporarily sealed with an impulse sealer to prepare a cell.
After temporarily sealing the three portions of the seal portions S1 to S3, an electrolytic solution having a predetermined mixing ratio is poured into the cell and dried under predetermined conditions. Then, as shown in FIG. The seal part including the seal part S4 was completely sealed with a vacuum sealer (FVS-7-400II manufactured by Furukawa Seisakusho).
As described above, electric double layer capacitor cells of Examples and Comparative Examples were produced.
In addition, about the mixing ratio of the electrolyte solution in each Example and a comparative example, and the drying conditions after temporary sealing are mentioned later.

Hereinafter, the types of electrolyte solutions, the presence / absence of drying, and conditions according to each example and comparative example will be described.
Example 1
In Example 1, 1-ethyl-3-methylimidazolium tetrafluoroborate (hereinafter referred to as EMIBF ₄ ) and methyl propionate (hereinafter referred to as MP) were mixed at 80:20 (volume%) for electrolysis. A liquid was prepared, 50 μl was poured into the temporarily sealed cell, and left for 4 hours and 50 minutes in a vacuum environment where the gauge pressure of the vacuum gauge was −0.09 MPa or less. The content of methyl propionate in the electrolyte after standing was 0.60% by weight.
And after standing, it completely sealed.

Example 2
An electrolytic solution in which EMIBF ₄ and acetone were mixed at a ratio of 80:20 (volume%) was poured into the cell and left under the same conditions as in Example 1.
The acetone content in the electrolyte after standing was 0.99% by weight.

Example 3
An electrolytic solution in which EMIBF ₄ and MP were mixed at 90:10 (volume%) was poured into the cell and left under the same conditions as in Example 1.
The content of MP in the electrolytic solution after standing was 0.22% by weight.

Example 4
An electrolytic solution in which EMIBF ₄ and MP were mixed at 95: 5 (volume%) was poured into the cell and left under the same conditions as in Example 1.
The content of MP in the electrolytic solution after being left was 0.14% by weight.

Comparative Example 1
Example 1 was repeated except that EMIBF ₄ alone was injected into the cell as an electrolyte.

Comparative Example 2
An electrolytic solution in which EMIBF ₄ and MP were mixed at 97: 3 (volume%) was poured into the cell and left under the same conditions as in Example 1. The content of MP in the electrolytic solution after standing was 0.13% by weight.

Comparative Example 3
EMIBF ₄ and methyl propionate were mixed at 80:20 (volume%) to prepare an electrolytic solution. In addition, the weight ratio of MP in electrolyte solution was 16.1 weight%.
After pouring the electrolyte prepared as described above into the cell, the pressure was reduced for 5 minutes in a vacuum environment with a gauge pressure of -0.07 MPa, and then returned to normal pressure and the gauge pressure was again reduced to -0.07 MPa. Thereafter, the pressure was reduced for 10 seconds, the pressure was returned to normal pressure, and the cell was completely sealed with a vacuum sealer. The weight percentage of MP after the impregnation operation was 10.3 wt%.

Comparative Example 4 (no organic solvent removal step)
EMIBF ₄ and MP were mixed at 98.7: 1.3 (volume%) to prepare an electrolytic solution. 50 μl of the prepared electrolyte was poured into the cell, and left for 4 hours and 50 minutes under atmospheric pressure. The content of MP in the electrolytic solution after standing was 1.00% by weight.
Thereafter, the cell was completely sealed with a vacuum sealer.
The surface tension of the ionic liquids and organic solvents used in Examples and Comparative Examples, was measured by the pendant drop method using an automatic surface tension meter PD-Z type manufactured by Kyowa Interface Science (Ltd.), EMIBF ₄ Was 54.4 mN / m (25 ° C.), acetone was 23.5 mN / m (25 ° C.), and MP (methyl propionate) was 24.4 mN / m (25 ° C.).

The following items were evaluated for the electric double layer capacitor cells of Examples 1 to 4 and Comparative Examples 1 to 4 produced as described above.
(1) Capacity measurement The capacity was measured as follows.
[Capacity measurement charge / discharge conditions]
The battery was charged by flowing a current of 10 mA until the voltage of each cell reached 2.75 V, then left for 10 seconds, and then discharged by flowing a current of 10 mA until the voltage of each cell reached 0.10 V. Left for 10 seconds.
This series of charging-leaving-discharging-leaving is defined as one cycle, and charging and discharging are performed for a total of 4 cycles, and then charging is performed by passing a current of 10 mA until the voltage of the electric double layer capacitor cell reaches 2.75 V. Then, the capacity (μWh) when discharged by flowing a current of 10 mA until the voltage of each cell reached 0.10 V was determined.
(2) Swelling evaluation under high temperature environment The electric double layer capacitor cell was placed in a thermostatic bath, and the swelling of the cell was confirmed after being left at 120 ° C. and a gauge pressure of a vacuum gauge of −0.09 MPa or less for 3 hours.

  The results of capacity measurement and cell swelling evaluation are shown in Table 2.

Table 2

As shown in Table 2, regarding the capacity, although the capacity of the electric double layer capacitor cell of Examples 1 to 4 is lower than that of the electric double layer capacitor cell of Comparative Example 3, the electric capacity of Comparative Examples 1, 2, and 4 is It was higher than the multilayer capacitor cell.
Further, comparing Example 4 with Comparative Example 1 in which the impregnation with the organic solvent and the removal of the organic solvent were not performed, the capacity of the electric double layer capacitor cell of Example 4 was increased by 5%.
Furthermore, although the electric double layer capacitor cell of Comparative Example 3 was excellent in electrochemical characteristics, the swelling of the cell was as large as 20% or more, and the reliability under a high temperature environment could not be satisfied.

The reason why excellent electrochemical characteristics were obtained in the electric double layer capacitor cell of Comparative Example 3 is considered as follows.
In Example 1, the remaining amount of MP is 0.22% by weight, whereas in Comparative Example 3, it is as high as 10.3% by weight. Thus, when the addition amount of the organic solvent increases with respect to the ionic liquid, the viscosity of the electrolytic solution decreases. As a result, a voltage is applied to the electric double layer capacitor cell, the resistance when the anion or cation moves in the electrolytic solution by electrophoresis decreases, and the ions easily move, and the conductivity of the electrolytic solution increases. .
As a result, the resistance of the electric double layer capacitor cell of Comparative Example 3 is considered to be low.
In the above capacitance measurement, if the resistance of the electric double layer capacitor cell is low, it takes time to reach 0.10 V, and the capacitance increases apparently.
Therefore, when charging and discharging is performed at a lower current, the capacities of Comparative Example 3 and Example 1 are estimated to be substantially the same.

  As described above, the electric double layer capacitor cells of Examples 1 to 4 have good electrochemical characteristics and can satisfy the reliability in a high temperature environment.

  In addition, it is preferable that content of the organic solvent in electrolyte solution is 50 volume% or less. When the content of the organic solvent in the electrolytic solution is 50% by volume or less, it is possible to inject 75% of the ionic liquid into the cell by repeating the injection step once or twice, but 50% by volume. If it exceeds 50%, the number of man-hours for injection increases, and the removal of the organic solvent takes time and productivity is deteriorated.

  In this embodiment, an example in which one cell assembly 50 is used has been described. However, the present invention is not limited to this, and a plurality of cell assemblies 50 are stacked to form an electric double layer capacitor cell. Of course, it can be applied to a wound type electric double layer capacitor cell.

  Further, in this embodiment, an example of an electric double layer capacitor cell has been shown, but the present invention is not limited to an electric double layer capacitor, and can be applied to an electricity storage device such as a lithium ion secondary battery or a lithium ion capacitor. .

  As described above, in an electricity storage device, it is effective to use an ionic liquid in order to improve heat resistance. However, an ionic liquid has a higher viscosity and lower conductivity than a commonly used electrolyte, Since the wettability with the active material used for the electrode is poor, the capacity reduction of the electricity storage device when using an ionic liquid has been a problem. However, according to the present invention, this difficult problem can be overcome, and it is possible to achieve both improvement in heat resistance and increase in capacity of the electricity storage device, which is of great industrial significance.

DESCRIPTION OF SYMBOLS 1 Active material layer 2 Electrolytic solution 10 Positive electrode plate 11 Activated carbon coating part of positive electrode plate 12 Lead part of positive electrode plate 20 Negative electrode plate 21 Activated carbon coating part of negative electrode plate 22 Lead part of negative electrode plate 30 Aramid separator 40 Laminate 41, 42 Kapton tape 50 Cell assembly 51 Positive electrode aluminum tab 52 Negative electrode aluminum tab 55 Conducting portion 60 Aluminum laminate film S1, S2, S3 Seal portion S4 Final seal portion

Claims (6)

A method of manufacturing an electricity storage device including an impregnation step of infiltrating an electrolytic solution into an active material layer,
The impregnation step comprises:
Mixing which infiltrates the active material layer with a mixed electrolyte of an ionic liquid and a high vapor pressure organic solvent that is compatible with the ionic liquid and has a lower surface tension than the ionic liquid and a higher vapor pressure than the ionic liquid An electrolytic solution impregnation step;
Removing a part or all of the high vapor pressure organic solvent from the permeated mixed electrolyte,
In the mixed electrolyte impregnation step, the content of the high vapor pressure organic solvent in the mixed electrolyte is adjusted to 5 vol% or more and 50 vol% or less,
In the removal step, the high-vapor pressure organic solvent content in the mixed electrolyte is removed so as to be 1% by weight or less.   The method for manufacturing an electricity storage device according to claim 1, wherein the high vapor pressure organic solvent has a vapor pressure at 20 ° C. of 8.5 kPa or more.   The method for producing an electricity storage device according to claim 1, wherein the high vapor pressure organic solvent has a boiling point of 80 ° C. or less.   The molecular weight of the said high vapor pressure organic solvent is 88.1 or less, The manufacturing method of the electrical storage device as described in any one of Claims 1-3 characterized by the above-mentioned.   The method for producing an electricity storage device according to any one of claims 1 to 4, wherein the high vapor pressure organic solvent has a surface tension at 25 ° C of 24.4 mN / m or less.   The method for manufacturing an electricity storage device according to any one of claims 1 to 5, wherein the high vapor pressure organic solvent is methyl propionate or acetone.

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